It is known that phenomena of various kinds are encountered during the production of a composite component having a final Z-section by laying up a plurality of layers of preimpregnated material, these phenomena being related to the process of polymerization in an autoclave with a vacuum bag, and being caused by the specific geometry of the metallic mould which shapes the component.
This is because the mould has a convex portion and a concave portion adjacent thereto, these portions being positioned so as to impart the desired Z-section to the component. Phenomena acting in opposite ways occur in these two portions during the autoclave process. In the concave portion, the laid-up structure tends to become thicker, while in the convex portion it tends to become thinner. This is caused by the migration of the resin contained in the laid-up structure, due to factors of local pressure variation.
To prevent the component from having local variations in thickness exceeding the specified tolerances, which may be 10% for example, at the end of the autoclave process, it is necessary to minimize the migration of resin due to local pressure variations, and also to remove and/or cause migration of the resin which would naturally tend to become denser in the concave portion.
In order to overcome the aforesaid problems, there has been a development of autoclave processes using moulds and counter-moulds, as well as processes having additional vacuum and/or heat stages, such as “hot forming” and “hot debulking” stages, used to reduce the flow of the resin.
In the first case, the apparatus used has the drawback of being complex and expensive, while in the second case the process is unfavourably complicated and takes a relatively long time to complete.